Patent GB-936324-A (GB)
Title: Improvements in or relating to braking systems
IPC: B60T8/18
Filed: 1961-12-27
Abstract: 936,324. Fluid-pressure brakes. D.B.A. S.A. Dec. 27, 1961 [Dec. 30, 1960], No. 46300/61. Class 103 (1). [Also in Group XXIX] In a compressed air or other fluid pressure braking system for a vehicle, fluid is supplied by a control valve to a brake cylinder via a brake pressure proportioning valve, which valve comprises a pressure-responsive means movable within a housing and having one area exposed to pressure at an inlet port of the housing and another area exposed to brake cylinder pressure existing at an outlet port of the housing, the latter area being arranged to be varied as a function of the position of the pressure responsive means within the housing, and a valve carried by the pressure-responsive means and actuated to connect or disconnect inlet and outlet ports by a valve actuating member movably mounted in the housing, whereby the outlet pressure for a given input pressure varies as a function of the position of the valve actuating member. As shown, a compressed air braking system comprises a reservoir 14 supplied by a pump 16, a driver's valve connected to the reservoir to provide a controlled pressure in line 20, a brake pressure proportioning valve 22 for each wheel of the vehicle connected between the line 20 and the respective brake cylinder 26, and a connection 29 between each valve 22 and corresponding bellows 28 of a pneumatic suspension system whereby the output pressure of the valve 22 for a given input pressure is automatically varied according to the load on the respective wheel. Each valve 22 has an inlet port from line 20, an outlet port 24 to the brake cylinder, and pressure-responsive means in the form of a plunger 42 to one end of which a diaphragm 50 is secured, the periphery of the diaphragm being secured to the housing so as to provide an outlet chamber 52, an intermediate chamber connected at 32 to atmosphere, and an inlet chamber 55. The plunger 42 has a valve opening 54 to connect the chambers 55, 52, a self-lapping valve assembly 58 being provided in association with this and another opening leading to the interior of a hollow valve actuating member 46 which is sealingly slidable in a partition 38 and comprises a piston 40 acted on by the pneumatic suspension pressure via inlet 36, in opposition to the force of a spring 48. The interior of member 46 is connected to atmosphere via ports 62, 34. When no pressure exists in line 20, a spring 56 maintains assembly 58 in a position to cause member 61 thereof to close the opening leading by way of the interior of member 46 to atmosphere, and a spring 64 maintains plunger 42 in a position such that valve opening 54 is clear of member 59 of the valve assembly. When pressure is supplied to line 20 it acts on diaphragm 50 with a greater force than that exerted on the face of the plunger exposed to the inlet pressure, so that the valve assembly 58 is lapped when the brake cylinder pressure reaches a corresponding fraction of the inlet pressure. If now the load on the wheel is increased, the correspondingly increased bellows pressure of the suspension moves piston 40 to compress spring 48 and move member 59 away from the valve opening 54, so that air passes into the chamber 52, causing plunger 42 to move to the left until the valve assembly is again lapped. Such movement of the plunger causes the diaphragm 50 to engage an inwardly directed conical face 53 of the housing to a gradually increasing extent as plunger 42 is moved by an increasing load towards its extreme position, Fig. 4, corresponding to maximum load, so that the effective area of the diaphragm is gradually decreased with increasing load, resulting in a corresponding increase in output pressure in chamber 52 for a given input pressure in chamber 55. On reduction of pressure in line 20 or/and decrease in load, valve member 61 opens the connection to atmosphere via ports 62, 34 to release the brake.